Melatonin is a hormone made by the pineal gland located in the human brain and can adjust wake/sleep cycles. When the photosensitive ganglion cells of the eyes receive blue light with a certain wavelength range, the brain will reduce the melatonin level in the body, resulting in the enhancement of alertness. Blue light sources, existing everywhere in our daily lives, seriously affect human's biological clock. Moreover, the current treatment for melatonin imbalance mainly uses medication. Therefore, it is required to control the percentage of blue light emitted by a display device according to our biological clocks.